The M109 is an American-made self-propelled 155 mm howitzer, first introduced in the early 1960s. It was upgraded a number of times to today’s M109A6 Paladin. The M109 family is the most common Western indirect-fire support weapon of maneuver brigades of armored and mechanized infantry divisions.
The M109 has a crew of six: the section chief, the driver, the gunner, the assistant gunner and two ammunition handlers. The gunner aims the cannon left or right (deflection), the assistant gunner aims the cannon up and down (quadrant). The M109A6 Paladin needs only one gunner and two ammunition handlers.
The British Army replaced its M109s with the AS-90. Several European armed forces have or are currently replacing older M109s with the German PzH2000, which outperforms the M109 in many aspects. Upgrades to the M109 were introduced by the U.S. (see variants below) and by Switzerland (KAWEST). With the cancellation of the U.S. Crusader, the Paladin remains the principal self-propelled howitzer for the U.S. for the foreseeable future.
The M109 was the medium variant of a U.S. program to adopt a common chassis for its self-propelled artillery units. The light version, the M108 Howitzer, was phased out during the Vietnam War, but many were rebuilt as M109s.
The M109 saw its combat debut in Vietnam. Israel used the M109 against Egypt in the 1973 Yom Kippur War and in the 1982 Lebanon War and 2006 Lebanon War. Iran used the M109 in the Iran–Iraq War, in the 1980s. The M109 saw service with the British Army, the Egyptian Army and Saudi Arabian Army in the 1991 Gulf War. The M109 also saw service with the U.S. Army in the Gulf War, as well as in the Iraq War from 2003 to present.
Upgrades to the cannon, ammunition, fire control, survivability, and other electronics systems over the design’s lifespan have expanded the system’s capabilities, including tactical nuclear projectiles, Cannon Launched Guided Projectiles (CLGP or Copperhead), Rocket Assisted Projectile (RAP), FAmily of SCAtterable Mines (FASCAM), and improved conventional munitions (the Dual-Purpose Improved Conventional Munition, DPICM).
The developing BCT Ground Combat Vehicle Program will likely replace the M109 as well as many other US army vehicles.
First produced in 1963, with 155 mm M126/A1 gun in the M127 Howitzer Mount, 28 rounds of 155 mm were carried. Also armed with a .50cal M2HB machine gun mounted, and 500 rounds of .50cal ammunition.
M109A1 and M109A1B
Replaced M126 with longer barreled M126A1 gun for greater effective range. Same M127 mount and ammunition amounts carried. A more recent model, intended for export incorporated more recent improvements into a new production M109A1. These were designated M109A1B.
Incorporated 27 Reliability, Availability, and Maintainability (RAM) mid-life improvements. Most notably, the long barreled 155 mm M185 cannon in the M178 gun mount, ballistic protection for the panoramic telescope, counterbalanced travel lock, and the ability to mount the M140 alignment device. Stowage increased from 28 rounds of 155 mm, to 36 rounds, .50cal ammunition amount remain 500 rounds.
M109A3 and M109A3B
M109A1s and M109A1Bs rebuilt to M109A2 standard respectively. Some A3s feature three contact arm assemblies while all A2s have five.
M109A2s and M109A3s improved with Nuclear, Biological, and Chemical / Reliability, Availability, and Maintainability (NBC/RAM) improvements, including air purifiers, heaters, and Mission Oriented Protective Posture (MOPP) gear.
The traversing mechanism’s clutch is hydraulic, as compared to the electric mechanism on previous M109s, and features a manual override in the event of an electrical failure. The A4 also adds an additional hydraulic filter, for a total of two. Also included, is an improvement to the engine starting equipment, greatly improving the ability to start in an emergency.
Ammunition amounts remain the same as two previous models.
Replaces M185 cannon in M178 mount with 155 mm M284 cannon in the M182 mount, giving the A5 even greater range than before.
Various manufacturers have upgraded the fire control and other components of the M109A5.
Overall product improvement in the areas of survivability, RAM, and armament. This includes increased armor, redesigned (safer) internal stowage arrangement for ammunition and equipment, engine and suspension upgrades, and product improvement of the M284 cannon and M182A1 mount. The greatest difference is the integration of an inertial navigation system, sensors detecting the weapons’ lay, automation, and an encrypted digital communication system which utilizes computer controlled frequency hopping to avoid enemy electronic warfare and allow the howitzer to send grid location and altitude to the battery fire direction center (FDC). The battery FDCs in turn coordinate fires through a battalion or higher FDC. This allows the Paladin to halt from the move and fire within 30 seconds with accuracy equivalent to the previous models when properly emplaced, laid, and safed — a process that required several minutes under the best of circumstances. Tactically, this improves the systems survivability by allowing the battery to operate dispersed by pairs across the countryside and allowing the howitzer to quickly displace between salvos, or if attacked by indirect fire, aircraft, or ground forces.
The performance of the M109A6 comparable to that of the first self-propelled artillery over the preceding towed artillery, since the howitzers are not fixed, but may move with the combat forces. They need stop only when a target is identified. After firing on a target, the Paladin is immediately able to resume movement.
Ammunition stowage is increased from 36 to 39 155 mm rounds.
This Swiss improved version produced by Ruag incorporates a new Swiss-designed L47 155 mm Gun with an increased firing range of up to 36 km. The L47 155 mm Gun is derived from the Swiss Bison fortress gun’s inertial navigation system coupled with a new gun-laying system and more ammunition storage. The KAWEST (lit. Kampfwertsteigerung = upgrade of combat capabilities) requires only 6 crew members instead of 8, and is able to fire 3-round bursts within 15 seconds or maintain a constant firing rate of over one round per minute. Technical modifications: Increased firing range of up to 27 km, increased rate of fire (burst of 3 rounds in 15 sec.), increased ammunition autonomy ( 40 rounds, 64 charges). New electrical system increases reliability (better than Mil STD 1245A, higher operational readiness, increased mean time between failures, fault-finding diagnostics with test equipment.) Integrated inertial navigation and positioning system, increased mobility (gears, engine), day and night operations capabilities, effective fire suppression system installed, NEMP and EMP protection. Camouflage: paint and netting. Upgraded Swiss PzHb (Panzerhaubitze) 79 and 88 (M109A1) are known as respectively PzHb 79/95 and PzHb 88/95.
Jointly developed by the Dutch firm RDM and the German firm Rheinmetall, the M109L52 was first revealed in 2002. The main improvement was replacing the M126 series gun with the longer
gun PzH 2000, so that the MTLS ammunition of the PzH 2000 can be used. In addition, improvements to the loading system were made. This resulted in an increase of the rate of fire to 9-10 rds/min from the original 3 rds/min, and this high rate of fire can be sustained for up to 2 minutes. A total of 35 rounds can be carried and trials have revealed that the M109L52 is 90% as effective as the PzH 2000, while the unit price of the M109L52 is only 15% to 30% of the PzH 2000. The M109L52 provides an attractive alternative to customers with financial constraints that prevent them from replacing older M109’s with the PzH 2000 on a one-to-one basis.
The replacement for the M109A6 in U.S. service is the M109 Paladin Integrated Managment (PIM).